RegEx Beginning of line or whitespace match

THRAK has asked for the wisdom of the Perl Monks concerning the following question:

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Re: RegEx Beginning of line or whitespace match by saintmike (Vicar) on Feb 11, 2005 at 21:37 UTC
Typically, the word boundary anchor `\b` works well in these cases: `if($line =~ /\bfor\(/) { # ... }` [download] It will also match `"(for("` and `";for("` which is a very common requirement for parsing programming languages. Speaking of which, if you are trying to parse perl or parts of it, check out PPI.	[reply] [d/l] [select]
Re^2: RegEx Beginning of line or whitespace match by THRAK (Monk) on Feb 11, 2005 at 21:46 UTC
See, I knew this wasn't as difficult to the level I was struggling with it. This works, because I forgot two additional test cases...that being that this could be anywhere in the line, not just at the beginning with or without spaces. e.g. `$line = 'could be anything here some_for($var)'; #don't match $line = 'could be anything here for($var)'; #match` [download] Thanks. -THRAK www.polarlava.com	[reply] [d/l]
Re^3: RegEx Beginning of line or whitespace match by CountZero (Bishop) on Feb 11, 2005 at 22:50 UTC
In other words: match if for( begins at a word boundary, don't match in all other cases: `m/\b(for\()/` PS: you can drop the parentheses if you don't want to extract anything and only want to test for matches. CountZero "If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law	[reply] [d/l]
Re: RegEx Beginning of line or whitespace match by eieio (Pilgrim) on Feb 11, 2005 at 21:33 UTC
`/^\s*(for\()/` should work. Use '^' to require that the match occurs at the beginning of a line rather than anywhere within the line.	[reply] [d/l]
Re: RegEx Beginning of line or whitespace match by gaal (Parson) on Feb 11, 2005 at 21:35 UTC
`/^\s*for\(/` This matches if the "for(" has no characters at all before it (== at beginning of line) or if there are whitespace characters. You were missing the anchor, I think.	[reply] [d/l]
Re: RegEx Beginning of line or whitespace match by Frantz (Monk) on Feb 11, 2005 at 21:33 UTC
try with this : `if ($line =~ /(\s+\|^)(for\()/gi) { print 'match'; }` [download]	[reply] [d/l]
Re^2: RegEx Beginning of line or whitespace match by ZlR (Chaplain) on Feb 12, 2005 at 17:22 UTC
I do not think the alternation of space with "start of line" is a good thing . It's not good style and it looks like it can cause problems. Use ^\s* instead . You don't need to remember the patterns so why use () to match the spaces ? What would the /g modifier do in such a context ? I don't like it with a start of line. Regards, ZlR.	[reply]
Re: RegEx Beginning of line or whitespace match by holli (Abbot) on Feb 11, 2005 at 21:38 UTC
`use strict; use diagnostics; my @line = ( 'some_for($var)', #don't match ' for($var)', #match 'for($var)', #match ); for ( @line ) { print /(^(\s+)?)for\(/gi ? "match\n" : "nomatch\n"; }` [download] holli, /regexed monk/	[reply] [d/l]
Re: RegEx Beginning of line or whitespace match by Anonymous Monk on Feb 12, 2005 at 15:04 UTC
Hi, simple try this `use strict; use diagnostics; my $line = 'some_for($var)'; #don't match $line = ' for($var)'; #match $line = 'for($var)'; #match if($line =~ m#^(\s+)?for\(#si) { print "Match"; } else { print "Non-match"; }` [download] Gubendran.L	[reply] [d/l]
Re: RegEx Beginning of line or whitespace match by gube (Parson) on Feb 12, 2005 at 15:05 UTC
Hi try this simple `use strict; use diagnostics; my $line = 'some_for($var)'; #don't match $line = ' for($var)'; #match $line = 'for($var)'; #match if($line =~ m#^(\s+)?for\(#si) { print "Match"; } else { print "Non-match"; }` [download] Gubendran.L	[reply] [d/l]